In industrial applications that involve flowing fluids, such as slurries, liquids, chemical, paper, pulp, petroleum, gas, pharmaceutical, food, mining, minerals and vapors and gasses in refinery, it is sometimes beneficial to know certain characteristics of the flowing fluids. For example, in the petroleum industry in which billions of dollars of crude oil are fiscally measured each day on its way from the well heads to the refineries, the volumetric flow rate is a critical measurement in process control and optimization. Unfortunately however, large amounts of hydrocarbons tend to be present in crude oil and as such, during transport between the well heads and the refineries the crude oil has a propensity to ‘out gas’ during transport resulting in small, unknown levels of entrained gases being present at the fiscal measurement locations. This is undesirable for at least two (2) reasons.
First, because the effect of the entrained gases on most known liquid volumetric technologies results in an over reporting of the liquid component flow rate by an amount equal to the volume of the entrained gases, the measured volumetric flow rate is typically inaccurate. In fact, standards have been imposed for volumetric flow. Unfortunately, however, while most standards for fiscal volumetric flow of liquids require that the liquid be completely devoid of gases, a problem arises when it becomes impractical to ensure that the liquid stream in question is indeed completely devoid of free gases. This is because although the gas volume fraction (GVF) level is typically less than 1%, it is often the primary source of error in the fiscal measurement. Second, because the complete separation of the gas and liquid phases cannot be ensured, the liquid volume determination is also typically inaccurate resulting in inaccurate watercut values. Thus, it is reasonable to expect that if more characteristics are known about the flowing fluid, there will be a better chance of effectively measuring, controlling, and optimizing the processing of the flowing fluid.
Accuracy of oil production measurement is limited to three constraints. One constraint involves the inability to ensure the complete separation of gas and liquid flow. This constraint results in an inaccurate liquid volume determination, inaccurate gas volume determination and an inaccurate watercut determination. The second constraint involves the relatively low number of flow measurements available due to maintenance requirements, installation requirements and pressure drop in the point with any increase in measurement points. The third constraint involves the very low number of watercut measurement points, which is due to the reliability of the watercut measurement devices and the calibration requirements of the meters.
Thus, it would be advantageous, particularly in the oil and production field, to have a reliable, non-intrusive, clamp-on apparatus capable of measuring the parameters of an aerated multiphase fluid flow, such as the volumetric flow rate liquid of the process flow, the gas volume (or void) fraction of the flow, the watercut of the flow, and the volumetric flow rate of each of the phases of the flow. The present invention provides such an apparatus.